Uses of natural energies have attracted attention in recent years. One of such uses is photovoltaic that converts solar energy into electric power through solar cells. As a photovoltaic device, there is well known a concentrating photovoltaic device having a configuration in which plural solar cell elements are arranged in a same plane, and condenser lenses (optical elements) configured to concentrate sunlight to the respective solar cell elements are arranged in front of the solar cell elements in order to increase the power generation efficiency (photoelectric conversion efficiency) for providing larger electric power (see Patent Literature 1, for example).
The concentrating photovoltaic device has a configuration in which each solar cell element receives sunlight concentrated by a condenser lens. Accordingly, the expensive solar cell elements can be reduced in size, and the photovoltaic device can be reduced in cost as a whole. The concentrating photovoltaic devices are therefore becoming widespread as power supply applications in areas which get many hours of sunshine and are vast enough for the photovoltaic devices to be installed even if the light collecting surface thereof is enlarged.